Implementing Static Routes for IPv6

First Published: June 7, 2001

Last Updated: January 28, 2011

This module describes how to configure static routes for IPv6. Routing defines the paths over which packets travel in the network. Manually configured static routes may be used instead of dynamic routing protocols for smaller networks or for sections of a network that have only one path to an outside network. Lack of redundancy limits the usefulness of static routes, and in larger networks manual reconfiguration of routes can become a large administrative overhead.

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the "Feature Information for Implementing Static Routes for IPv6" section.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn.An account on Cisco.com is not required.

Prerequisites for Implementing Static Routes for IPv6

•This document assumes that you are familiar with IPv4. Refer to the publications referenced in the "Related Documents" section for IPv4 configuration and command reference information.

•Before configuring the router with a static IPv6 route you must enable the forwarding of IPv6 packets using the ipv6 unicast-routing global configuration command, enable IPv6 on at least one interface, and configure an IPv6 address on that interface. For details on basic IPv6 connectivity tasks, refer to the Implementing Ipv6 Addressing and Basic Connectivity module.

Information About Implementing Static Routes for IPv6

Static Routes

Networking devices forward packets using route information that is either manually configured or dynamically learned using a routing protocol. Static routes are manually configured and define an explicit path between two networking devices. Unlike a dynamic routing protocol, static routes are not automatically updated and must be manually reconfigured if the network topology changes. The benefits of using static routes include security and resource efficiency. Static routes use less bandwidth than dynamic routing protocols and no CPU cycles are used to calculate and communicate routes. The main disadvantage to using static routes is the lack of automatic reconfiguration if the network topology changes.

Static routes can be redistributed into dynamic routing protocols but routes generated by dynamic routing protocols cannot be redistributed into the static routing table. No algorithm exists to prevent the configuration of routing loops that use static routes.

Static routes are useful for smaller networks with only one path to an outside network and to provide security for a larger network for certain types of traffic or links to other networks that need more control. In general, most networks use dynamic routing protocols to communicate between networking devices but may have one or two static routes configured for special cases.

Directly Attached Static Routes

In directly attached static routes, only the output interface is specified. The destination is assumed to be directly attached to this interface, so the packet destination is used as the next-hop address. This example shows such a definition:

ipv6 route 2001:DB8::/32 ethernet1/0

The example specifies that all destinations with address prefix 2001:DB8::/32 are directly reachable through interface Ethernet1/0.

Directly attached static routes are candidates for insertion in the IPv6 routing table only if they refer to a valid IPv6 interface; that is, an interface that is both up and has IPv6 enabled on it.

Recursive Static Routes

In a recursive static route, only the next hop is specified. The output interface is derived from the next hop. This example shows such a definition:

ipv6 route 2001:DB8::/32 2001:DB8:3000:1

This example specifies that all destinations with address prefix 2001:DB8::/32 are reachable via the host with address 2001:DB8:3000:1.

A recursive static route is valid (that is, it is a candidate for insertion in the IPv6 routing table) only when the specified next hop resolves, either directly or indirectly, to a valid IPv6 output interface, provided the route does not self-recurse, and the recursion depth does not exceed the maximum IPv6 forwarding recursion depth.

A route self-recurses if it is itself used to resolve its own next hop. For example, suppose we have the following routes in the IPv6 routing table:

IPv6 Routing Table - 9 entries

Codes: C - Connected, L - Local, S - Static, R - RIP, B - BGP

U - Per-user Static route

I1 - ISIS L1, I2 - ISIS L2, IA - ISIS interarea

O - OSPF intra, OI - OSPF inter, OE1 - OSPF ext 1, OE2 - OSPF ext 2

R 2001:DB8::/32 [130/0]

via ::, Serial2/0

B 2001:DB8:3000:0/16 [200/45]

Via 2001:DB8::0104

The following examples defines a recursive IPv6 static route:

ipv6 route

2001:DB8::/32 2001:0BD8:3000:1

This static route will not be inserted into the IPv6 routing table because it is self-recursive. The next hop of the static route, 2001:DB8:3000:1, resolves via the BGP route 2001:DB8:3000:0/16, which is itself a recursive route (that is, it only specifies a next hop). The next hop of the BGP route, 2001:DB8::0104, resolves via the static route. Therefore, the static route would be used to resolve its own next hop.

It is not normally useful to manually configure a self-recursive static route, although it is not prohibited. However, a recursive static route that has been inserted in the IPv6 routing table may become self-recursive as a result of some transient change in the network learned through a dynamic routing protocol. If this occurs, the fact that the static route has become self-recursive will be detected and it will be removed from the IPv6 routing table, although not from the configuration. A subsequent network change may cause the static route to no longer be self-recursive, in which case it will be reinserted in the IPv6 routing table.

Note In Cisco IOS Release 12.2(15)T and older releases, IPv6 recursive static routes are checked at one-minute intervals. Therefore, a recursive static route may take up to a minute to be inserted into the routing table once its next hop becomes valid. Likewise, it may take a minute or so for the route to disappear from the table if its next hop becomes invalid.

Fully Specified Static Routes

In a fully specified static route, both the output interface and the next hop are specified. This form of static route is used when the output interface is a multi-access one and it is necessary to explicitly identify the next hop. The next hop must be directly attached to the specified output interface. The following example shows a definition of a fully specified static route:

ipv6 route 2001:DB8:/32 ethernet1/0 2001:DB8:3000:1

A fully specified route is valid (that is, a candidate for insertion into the IPv6 routing table) when the specified IPv6 interface is IPv6-enabled and up.

Floating Static Routes

Floating static routes are static routes that are used to back up dynamic routes learned through configured routing protocols. A floating static route is configured with a higher administrative distance than the dynamic routing protocol it is backing up. As a result, the dynamic route learned through the routing protocol is always used in preference to the floating static route. If the dynamic route learned through the routing protocol is lost, the floating static route will be used in its place. The following example defines a floating static route:

ipv6 route 2001:DB8:/32 ethernet1/0 2001:DB8:3000:1 210

Any of the three types of IPv6 static routes can be used as a floating static route. A floating static route must be configured with an administrative distance that is greater than the administrative distance of the dynamic routing protocol, because routes with smaller administrative distances are preferred.

Note By default, static routes have smaller administrative distances than dynamic routes, so static routes will be used in preference to dynamic routes.

Sample Output from the show ipv6 static Command with the IPv6 Address and Prefix Command

When the ipv6-address or ipv6-prefix/prefix-length argument is specified, only information about static routes for that address or network is displayed. The following is sample output from the show ipv6 static command when entered with the IPv6 prefix 2001:DB8:200::/35:

Router# show ipv6 static 2001:DB8:5555:0/16

IPv6 Static routes

Code: * - installed in RIB

* 2001:DB8:5555:0/16, via nexthop 2001:DB8:4000:1, distance 1

2001:DB8:5555:0/16, via nexthop 2001:9999:1, distance 2

* 2001:DB8:5555:0/16, interface Ethernet2/0, distance 1

Sample Output from the show ipv6 static interface Command

When an interface is supplied, only those static routes with the specified interface as outgoing interface are displayed. The interface keyword may be used with or without the IPv6 address and prefix specified in the show ipv6 static command.

Router# show ipv6 static interface ethernet3/0

IPv6 Static routes

Code: * - installed in RIB

Sample Output from the show ipv6 static recursive Command

When the recursive keyword is specified in the show ipv6 static command, only recursive static routes are displayed. The recursive keyword is mutually exclusive with the interface keyword, but it may be used with or without the IPv6 prefix included in the command syntax.

Router# show ipv6 static recursive

IPv6 Static routes

Code: * - installed in RIB

* 2001:DB8:4000:0/16, via nexthop 2001:DB8:1:1, distance 1

* 2001:DB8:5555:0/16, via nexthop 2001:DB8:4000:1, distance 2

2001:DB8:5555:0/16, via nexthop 2001:DB8:9999:1, distance 3

Sample Output from the show ipv6 static detail Command

When the detail keyword is specified, the following additional information is also displayed:

In the following example, the show ipv6 route command is used to verify the configuration of a static route through a point-to-point interface:

Router# show ipv6 route

IPv6 Routing Table - 9 entries

Codes: C - Connected, L - Local, S - Static, R - RIP, B - BGP

U - Per-user Static route

I1 - ISIS L1, I2 - ISIS L2, IA - ISIS interarea

O - OSPF intra, OI - OSPF inter, OE1 - OSPF ext 1, OE2 - OSPF ext 2

S 2001:DB8::/32 [1/0]

via ::, Serial2/0

In the following example, the show ipv6 route command is used to verify the configuration of a static route on a multiaccess interface. An IPv6 link-local address—FE80::1—is the next-hop router.

Router# show ipv6 route

IPv6 Routing Table - 11 entries

Codes: C - Connected, L - Local, S - Static, R - RIP, B - BGP

U - Per-user Static route

I1 - ISIS L1, I2 - ISIS L2, IA - ISIS interarea

O - OSPF intra, OI - OSPF inter, OE1 - OSPF ext 1, OE2 - OSPF ext 2

S 2001:DB8::/32 [1/0]

via FE80::1, Ethernet0/0

To display all static routes in the IPv6 routing table, use the show ipv6 route static command is used with static as the value of the protocol argument:

Router# show ipv6 route static

IPv6 Routing Table - 330 entries

Codes: C - Connected, L - Local, S - Static, R - RIP, B - BGP

U - Per-user Static route

I1 - ISIS L1, I2 - ISIS L2, IA - ISIS interarea

S 2001:DB8::/32 [1/0]

via ::, Tunnel0

S 3FFE:C00:8011::/48 [1/0]

via ::, Null0

S ::/0 [254/0]

via 2001:DB8:2002:806B, Null

Sample Output from the debug ipv6 routing Command

In the following example, the debug ipv6 routing command is used to verify the installation of a floating static route into the IPv6 routing table when an IPv6 RIP route is deleted. The floating static IPv6 route was previously configured with an administrative distance value of 130. The backup route was added as a floating static route because RIP routes have a default administrative distance of 120, and the RIP route should be the preferred route. When the RIP route is deleted, the floating static route is installed in the IPv6 routing table.

Example: Configuring Manual Summarization

The following example shows a static route being used to summarize local interface prefixes advertised into RIP. The static route also serves as a discard route, discarding any packets received by the router to a 2001:DB8:1::/48 destination not covered by a more specific interface prefix.

Router> enable

Router# configure terminal

Enter configuration commands, one per line. End with CNTL/Z.

Router(config)# interface ethernet0/0

Router(config-if)# ipv6 address 2001:DB8:2:1234/64

Router(config-if)# exit

Router(config)#

Router(config)# interface ethernet1/0

Router(config-if)# ipv6 address 2001:DB8:3:1234/64

Router(config-if)# exit

Router(config)# interface ethernet2/0

Router(config-if)# ipv6 address 2001:DB8:4:1234/64

Router(config-if)# exit

Router(config)# interface ethernet3/0

Router(config-if)# ipv6 address 2001:DB8::1234/64

Router(config-if)# ipv6 rip one enable

Router(config-if)# exit

Router(config)# ipv6 router rip one

Router(config-rtr)# redistribute static

Router(config-rtr)# exit

Router(config)# ipv6 route 2001:DB8:1:1/48 null0

Router(config)# end

00:01:30: %SYS-5-CONFIG_I: Configured from console by console

Router# show ipv6 route static

IPv6 Routing Table - 3 entries

Codes: C - Connected, L - Local, S - Static, R - RIP, B - BGP

U - Per-user Static route

I1 - ISIS L1, I2 - ISIS L2, IA - ISIS interarea, IS - ISIS summary

O - OSPF intra, OI - OSPF inter, OE1 - OSPF ext 1, OE2 - OSPF ext 2

ON1 - OSPF NSSA ext 1, ON2 - OSPF NSSA ext 2

S 2001:DB8:1::/48 [1/0]

via ::, Null0

Example: Configuring Traffic Discard

Configuring a static route to point at interface null0 may be used for discarding traffic to a particular prefix. For example, if it is required to discard all traffic to prefix 2001:DB8:42:1/64, the following static route would be defined:

Router> enable

Router# configureterminal

Enter configuration commands, one per line. End with CNTL/Z.

Router(config)# ipv6 route 2001:DB8:42:1::/64 null0

Router(config)# end

Example: Configuring a Fixed Default Route

A default static route is often used in simple router topologies. In the following example, a router is connected to its local site via Ethernet0/0 and to the main corporate network via Serial2/0 and Serial3/0. All nonlocal traffic will be routed over the two serial interfaces.

Router(config)# interface ethernet0/0

Router(config-if)# ipv6 address 2001:DB8:17:1234/64

Router(config-if)# exit

Router(config)# interface Serial2/0

Router(config-if)# ipv6 address 2001:DB8:1:1234/64

Router(config-if)# exit

Router(config)# interface Serial3/0

Router(config-if)# ipv6 address 2001:DB8:2:124/64

Router(config-if)# exit

Router(config)# ipv6 route ::/0 Serial2/0

Router(config)# ipv6 route ::/0 Serial3/0

Router(config)# end

Router#

00:06:30: %SYS-5-CONFIG_I: Configured from console by console

Router# show ipv6 route static

IPv6 Routing Table - 7 entries

Codes: C - Connected, L - Local, S - Static, R - RIP, B - BGP

U - Per-user Static route

I1 - ISIS L1, I2 - ISIS L2, IA - ISIS interarea, IS - ISIS summary

O - OSPF intra, OI - OSPF inter, OE1 - OSPF ext 1, OE2 - OSPF ext 2

ON1 - OSPF NSSA ext 1, ON2 - OSPF NSSA ext 2

S ::/0 [1/0]

via ::, Serial2/0

via ::, Serial3/0

Example: Configuring a Floating Static Route

A floating static route often is used to provide a backup path in the event of connectivity failure. In the following example, the router has connectivity to the network core via Serial2/0 and learns the route 2001:DB8:1:1/32 via IS-IS. If the Serial2/0 interface fails, or if route 2001:DB8:1:1/32 is no longer learned via IS-IS (indicating loss of connectivity elsewhere in the network), traffic is routed via the backup ISDN interface.

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RFCs

Title

No new or modified RFCs are supported by this feature, and support for existing RFCs has not been modified by this feature.

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Feature Information for Implementing Static Routes for IPv6

Table 13 lists the features in this module and provides links to specific configuration information.

Use Cisco Feature Navigator to find information about platform support and software image support. Cisco Feature Navigator enables you to determine which software images support a specific software release, feature set, or platform. To access Cisco Feature Navigator, go to http://www.cisco.com/go/cfn. An account on Cisco.com is not required.

Note Table 13 lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

Static routes are manually configured and define an explicit path between two networking devices.

This entire document provides information about this feature.

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